Facts of the Matter
STAR-BULLETIN / 1997
A 95-foot-high wave nearly caused the Queen Elizabeth II to capsize in the North Atlantic.
Missing ships might have been lost to rogue waves
SINCE PEOPLE first ventured out onto the ocean, sailors have returned from voyages telling of "holes in the sea" and monstrous waves. Their stories have largely been dismissed as tall tales until recently.
Even now, a ship is lost at sea every week, and not small ones; 200 ships lost in the past 20 years have been more than 650 feet long. Unlike heavily investigated airplane crashes, there is often little or no evidence left behind and no information about the reasons behind the losses. They are simply blamed on bad weather or human error.
The stories of the old salts are gaining credence with scientific documentation of rogue waves, which are now suspected to be the cause of the sinking and mysterious disappearances of many ships.
Until recently, scientists thought they could predict the heights of ocean waves using the "linear model," which defines the probabilities of certain wave heights from measured heights.
The distribution is a Rayleigh distribution rather than the more common bell curve of a normal distribution. A Rayleigh distribution is skewed toward the lower end such that the peak of the curve is at a lower height than the average; there are significantly more waves lower than the average than there are waves higher than the average.
Except for tsunami or surface disturbances, water waves are generated by wind. In the linear model, the distribution of wave heights is a function of the wind speed and the time that the wind blows over a certain stretch of water.
Recording the heights, wavelengths and frequencies of waves on a choppy sea surface is a difficult task and was done until recently by "eye" from the pitching, rolling and yawing deck of ship. Modern equipment on the stationary platforms of offshore drilling platforms has allowed for the measurement and continuous recording of wave heights.
At any given time and place, waves of different characteristics are coming from all directions, having been generated by local winds and by winds from storms halfway around the world.
Even within a stormy region, the speed and direction of wind and gusts changes from minute to minute, making prediction of wave heights impossible, so the linear model was the best that was available.
In the linear model, wave heights of given "sea" are reported as the significant wave height (SWH), which is the average height of the highest one-third of waves.
The Rayleigh distribution of the linear model predicts that the most frequent waves will have a height about 50 percent of the SWH, the average waves will have a height about 60 percent of the SWH and the highest 10 percent of waves will be about 25 percent higher than the SWH.
A "rogue" wave is now defined as any wave that is more than double the SWH, which the Rayleigh distribution predicts should occur only in about one wave out of every 3,000.
On Jan. 1, 1995, the Draupner oil platform in the North Sea off Norway electronically recorded a 95-foot wave during a storm with SWH of approximately 40 feet. The wave caused minor damage on the platform, confirming that the reading was valid.
According to the linear model, a wave of this size should occur in 40-foot seas only once in every 10,000 years.
The Draupner wave was the first positively confirmed rogue wave and the first to cast aspersions on the validity of the linear model with reliable measurement.
Since then other reliable reports have come from several sources.
In February 1995 the cruise liner Queen Elizabeth II encountered a 95-foot wave during in the North Atlantic that her captain described as "a great wall of water -- it looked as if we were going into the White Cliffs of Dover." He estimated that the ship listed so far that five inches more would have caused it to capsize.
Within a week between in late February and early March 2001, 100-foot waves in the South Atlantic smashed the bridge windows of two cruise ships, the Bremen and the Caledonian Star. The Bremen drifted parallel to the waves without navigation or propulsion for two hours before the engines were started and power restored.
Radar data from the North Sea's Goma oilfield showed 466 rogue wave encounters in 12 years and stimulated interest among skeptical scientists and engineers who had previously relied on the linear model for designing drilling platforms and ships to withstand maximum wave heights of only 50 feet.
In April 2005 a wave estimated to be 70 feet high smashed windows on the ninth and 10th decks of the Norwegian Dawn off the Florida coast. A company spokeswoman told reporters that the sea had calmed down after a storm when the wave seemed to "come out of thin air" at daybreak. The ship's captain, who has 20 years on the job, said he had never seen anything like it.
As more data are collected, it appears that rogue waves occur multiple times in a given week somewhere in the world.
In December 2000 the European Space Agency began a project (MaxWave) to monitor and model the occurrence of rogue waves. ESA scientists used radar satellite data with a resolution of 30 feet to conduct a global rogue wave census.
Over a three-week period in 2001, they identified more than 10 individual rogue waves greater than 80 feet in height, a shocking revelation that showed rogue waves to be very real and much more common than anyone expected.
Scientists are beginning to draw patterns. Sites where ordinary waves encounter ocean currents and eddies can concentrate wave energy in a small area, such as where the Gulf Stream interacts with waves coming in from the Labrador Sea in the northern Atlantic Ocean between eastern Canada and southwest Greenland.
This is the where the Andrea Gail, made famous by the 2001 movie "The Perfect Storm," was lost during an unusually intense nor'easter.
Sustained winds can enlarge waves moving in sync with the wind in the vicinity of weather fronts and low-pressure centers to generate rogue waves.
Unfortunately, satellite research shows that rogue waves also occur in areas that are not affected by currents, geographical formations or weather. Such "random" rogue waves are more problematic because they are unpredictable.
Wave mathematicians are delving into nonlinear quantum mechanics for solutions to model how some waves steal energy from neighboring waves to grow into "holes" and steep rogue waves.
picks up where your high school science teacher left off. He is a professor of science at Honolulu Community College, where he teaches earth and physical science and investigates life and the universe. He can be reached by e-mail at firstname.lastname@example.org